It is with some surprise that I admit that I actually went through and looked at all 806 of the Victorian era sheet music covers in Reading University's Spellman Collection via the wonderful Arts and Humanities Data Service (AHDS) Visual Arts University College, UK. The vast majority are described as 'humorous' and quite a few are really funny. Never let it be said that Victorian Britain did not have a sense of
Put 'Spellman Collection' in the image search box - results are thumbnail pages. [link updated March 2015]
Previously: American sheet music covers.